Heretofore, automotive drivelines employ a constant-velocity joint for connecting a transmission shaft to another transmission shaft and transmitting rotational power to the axles.
One conventional constant-velocity joint, whose technical concept is disclosed in Japanese Laid-Open Patent Publication No. 10-184717, has, as shown in FIG. 21 of the accompanying drawings, a roller 1 having a cylindrical inner circumferential wall surface 2 and a pair of flanges (not shown) mounted on the respective axial ends of the cylindrical inner circumferential wall surface 2 for preventing rolling elements 3 (rolls, needles, or the like) from being dislodged. The constant-velocity joint is assembled as follows: A plurality of rolling elements 3, whose number is one less than the total number of rolling elements 3 to be finally mounted, is arrayed between the flanges on the cylindrical inner circumferential wall surface 2. The dimensions of the cylindrical inner circumferential wall surface 2 and the rolling elements 3 are selected such that the minimum distance d2 between two rolling elements 3 on the ends of the array is smaller than the diameter d1 of a rolling element 3a which is to be added finally between those two rolling elements 3 (d2<d1). The difference between the distance d2 and the diameter d1 (d1−d2) serves as an interference ranging from several μm to several tens μm. Then, the rolling element 3a is finally pressed in between the two rolling elements 3 radially outwardly toward the cylindrical inner circumferential wall surface 2, thus installing the rolling elements 3 on the cylindrical inner circumferential wall surface 2.
The above process of arraying the rolling elements 3 along the cylindrical inner circumferential wall surface 2 of the roller 1 is referred to as a keystone process. The keystone process allows the roller 1 and the rolling elements 3 to be integrally combined as an inseparable assembly which is assembled on a leg shaft.
If the process of assembling the rolling elements 3 as disclosed in Japanese Laid-Open Patent Publication No. 10-184717 is applied and the rolling elements 3, whose number is one less than the total number of rolling elements 3 to be finally mounted, are to be arrayed successively one by one between the flanges along the cylindrical inner circumferential wall surface 2 of the circumferentially rotating roller 1, not manually, but by a mechanism (not shown) such as a cam or the like, then circumferential clearances may occur between the rolling elements 3 arrayed along the cylindrical inner circumferential wall surface 2, or clearances developed between the rolling elements 3 arrayed along the cylindrical inner circumferential wall surface 2 may become irregular.
Even if the final rolling element 3a is pressed in between the two rolling elements 3 radially outwardly toward the cylindrical inner circumferential wall surface 2, since the actual interference is greater than the preset interference due to the clearances, it is difficult to press the final rolling element 3a neatly into place or the rolling elements 3, 3a are deformed when the final rolling element 3a is forcibly pressed into place.
According to the process of assembling rolling elements as disclosed in Japanese Laid-Open Patent Publication No. 10-184717, when the final rolling element 3a is pressed into the gap between the two rolling elements 3, as shown in FIG. 21, the radially outward pressing force concentrates on the final rolling element 3a. Therefore, a holder 4 needs to be positioned on the outer circumferential surface of the roller 1 for bearing the radially outward pressing force acting on the final rolling element 3a. As a result, the number of parts making up an assembling apparatus that performs the process of assembling rolling elements is increased, resulting in an increase in the cost to manufacture the constant-velocity joint.
There have heretofore been employed various bearings to meet various load requirements including different load magnitudes, directions, and rotational speeds. Those various bearings are generally classified into radial bearings and thrust bearings according to the directions of loads to be borne. One of the radial bearings for bearing radial loads is known as a keystone bearing.
The keystone bearing is a radial bearing for use under heavy loads, and has a basic structure including an annular array of rolling elements in the form of cylindrical rolls arranged fully circumferentially in contact with the inner surface of an outer race. The keystone bearing does not require a retainer for preventing the cylindrical rolls from being dislodged. The keystone bearing has a member for keeping the rolling elements within the outer race against dislodgment during operation, the member having an inside diameter smaller than a minimum dimension from which the rolling elements would be dislodged radially inwardly.
A conventional keystone bearing as disclosed in Japanese Laid-Open Utility Model Publication No. 2-9329 is also illustrated in FIG. 21 of the accompanying drawings. As shown in FIG. 21, the keystone bearing includes an outer race 1 having a cylindrical inner circumferential wall surface 2 and a pair of flanges (not shown) mounted on the respective axial ends of the cylindrical inner circumferential wall surface 2 for preventing rolling elements 3 (rolls, needles, or the like) from being dislodged. The constant-velocity joint is assembled as follows: A plurality of rolling elements 3, whose number is one less than the total number of rolling elements 3 to be finally mounted, is arrayed between the flanges on the cylindrical inner circumferential wall surface 2. The dimensions of the cylindrical inner circumferential wall surface 2 and the rolling elements 3 are selected such that the minimum distance d2 between two rolling elements 3 on the ends of the array is smaller than the diameter d1 of a rolling element 3a which is to be added finally between those two rolling elements 3 (d2<d1). Then, the rolling element 3a is finally pressed in between the two rolling elements 3 radially outwardly toward the cylindrical inner circumferential wall surface 2, thus installing the rolling elements 3 on the cylindrical inner circumferential wall surface 2. Japanese Utility Model Publication No. 7-53865 discloses a bearing rolling element assembling apparatus which employs an eccentric cam.